The present invention relates to intraocular lenses, and more particularly, to improved haptics therefor.
Intraocular lenses are employed as replacements for the crystalline lens after either extracapsular or intracapsular surgery for the removal of a cataract. Intraocular lenses are generally of two types, those that are placed in the anterior chamber, i.e., between the iris and cornea, and those that are placed in the posterior chamber, i.e., behind the iris. Both types of lenses are conventionally employed with a choice between an anterior and a posterior lens being partly dictated by requirements of the patient and partly dictated by the preferences of the physician inserting the lens.
Intraocular lenses normally consist of an optic with two or more haptics that extend generally radially from the optic and contain foot portions that normally seat in the scleral spur for an anterior lens and either in the ciliary sulcus or within the lens capsule for a posterior lens. The optic normally comprises a circular transparent optical lens. The haptic in most lenses is a flexible fiber or filament having one end affixed to the lens and having a second portion extending radially away from the lens to form the seating foot. Several haptic designs are currently in use, for example, a pair of U-shaped loops in which both ends of each loop are connected to the lens and, for example, J-shaped loops in which only one end of the loop is affixed to the lens.
When anterior lenses are employed, care must be taken when inserting the lens and seating the haptics in the scleral spur that the lens itself does not move forwardly so that it contacts the endothelial lining on the posterior side of the cornea. Contact with the endothelial layer is detrimental because destruction of too many endothelial cells will result in corneal decompensation and subsequent opacification of the cornea. One of the drawbacks of conventional anterior lens designs is that when the flexible haptics are compressed, the lens is thrust forwardly along the optical axis. This reaction of the optic to haptic compression causes the optic to move forwardly toward and possibly to contact the endothelial layer as the lens is being inserted. Moreover, once the lens is inserted, if the eye is distorted, for example, by an accidental blow, the haptics can be compressed, vaulting the optic forwardly into the endothelial layer. One solution to vaulting is the use of posterior lenses. However, there are still situations when use of an anterior lens is dictated or desired.
One suggested solution for eliminating vaulting in anterior chamber lens is contained in U.S. Pat. No. 4,316,293 to John H. Bayers. Bayers suggests the use of a haptic having a symmetrical cross section with a minor dimension and a major dimension, the major dimension being oriented generally parallel to the axis of the optic. According to Bayers, this haptic configuration will allow the haptic to flex only in the direction of the minor axis, i.e., generally in the direction perpendicular to the major axis of the haptic. Thus, according to Bayers, whether the haptics are compressed for insertion or by an accidental blow to the eye or for any other reason, the haptics will spread only outwardly from each other and in theory alleviate the vaulting problem.
It has been found, however, that with haptics having a cross section as suggested by Bayers, for example, and oval cross section, the optic still vaults, that is, moves along the optical axis as the haptics are compressed. Moreover, the legs of the Bayers' haptics, that is the portions of the haptics extending from the lens to the seating portions of the haptics tend to move laterally in the same direction, causing the optic to move sideways relative to the optic axis. At the same time, the haptic may twist, causing the lens to rotate about an axis generally perpendicular to the optical axis. All three of these tendencies, i.e., the vaulting, the sideward movement, and the twisting are undesirable not only during insertion, but also once the lens has been implanted.